Field of the Invention
The present invention relates to a lens barrel.
Related Background Art
As disclosed in, e.g., Japanese Patent Application Laid-Open No. 3-209412, a known lens barrel has hitherto been constructed in the following manner. A rotary drum is rotatably fitted in a fixed drum. At the same time, the rotary drum incorporates a lens drum for accommodating lenses. With a rotation of the rotary drum, the lens drum is movable in the optical-axis direction of the lenses.
In the conventional lens barrel described above, however, only a portion of the rotary drum on the side of a film surface is fitted to the fixed drum, whereas a subject-side portion thereof is not fitted to the fixed drum. The rotary drum may therefore be tilted with respect to the fixed drum. This causes a possibility in which the lens drum accommodating the lenses may be tilted. Further, there is a probability wherein when a gear formed on the subject-side portion of the rotary drum is rotated by a driving gear, a sufficient moment is generated to exert a load on the rotation of the rotary drum.
In the conventional lens barrel, the lens drum is hard to locate in a predetermined initial position due to working and assembling errors, etc. Therefore, the following practice has been conducted. During a manufacturing process, as illustrated in FIG. 6, a lens drum 215 of a camera 213 is disposed upwards on a horizontal specular surface 211. A beam B is incident on the lens drum 215, and the light reflected by the specular surface 211 is measured. Based on this measurement, a position of the lens drum 215 is adjusted. In this case, according to the conventional lens barrel, the positional adjustment of the lens drum 215 is allowed to be effected only from the rear surface of the camera 213. The camera 213 has to be turned over. This leads to a problem that a large number of working steps are required for the positional adjustment of the lens drum 215.
Another type of lens barrel is constructed to move the lens in the optical-axis direction by relatively rotating a pair of cam drums coaxially arranged.
This type of known lens barrel is disclosed in, e.g., Japanese Patent Application Laid-Open No. 63-98638. The following is an explanation of this lens barrel with reference to FIG. 7.
As depicted in FIG. 7, the lens barrel shown in the above-mentioned publication includes a first cam drum 1, a second cam drum 2, a lens holder 4, a spring 6 and a cam stop ring 8. The first cam drum 1 is formed with three rectilinear slots 1a cut in the radial direction and extending in parallel to the axial line. The second cam drum 2 is fitted to the outer periphery of the first cam drum 1 and formed with three helical slots 2a (only two slots are shown in the Figure) helically cut in the inner peripheral surface about the axial line. A lens 3 is secured to the inner periphery of the lens holder 4 fitted to the inner periphery of the first cam drum 1. The cam pins 5 protrude from the outer periphery of the lens holder 4 and pass through the rectilinear slots 1a of the first cam drum 1. Tips of the cam pins 5 engage with the helical slots 2a of the second cam drum 2. The spring 6 is arranged between a flange 1b of the first cam drum 1 and the lens holder 4. The spring 6 pushes the cam pins 5 against the helical slots 2a. The cam stop ring 8 secured to the flange 1b of the first cam drum 1 prevents the second cam drum 2 from coming off in the axial direction due to a resilient force of the spring 6. When the second cam drum 2 is rotated about the first cam drum 1, the cam pins 5 are thrust out in the optical-axis direction of the lens 3 in accordance with the helix angle of each of the helical slots 2a. The lens holder 4 then moves in the optical-axis direction. A focal distance of the lens 3 is thus adjusted.
In the lens barrel described above, the rectilinear slots 1a of the first cam drum 1 and the helical slots 2a of the second cam drum 2 are both formed in the end surfaces 1c, 2c of these cam drums 1, 2 that face in the assembling direction. With this arrangement, when assembling the lens holder 4 and the second cam drum 2 to the first cam drum 1, the cam pins 5 are attached to the outer periphery of the lens holder 4. Thereafter, the lens holder 4 is inserted into the first cam drum 1. Then, the second cam drum 2 may be covered thereon. The work is thereby facilitated.
Where the rectilinear slots of the first cam drum 1 are formed in the end surface 1c, however, the end portions of the first cam drum 1 are split in the peripheral direction enough to decrease a rigidity thereof. These end portions may thus deform in the radial direction and rub against the lens holder 4 and the second cam drum 2 as well. The actions of the lens holder 4 and the second cam drum 2 may become unsmooth in some cases.
To obviate this defect, if the rectilinear slots 1a are formed as elongate holes without being cut in the end surface 1c, the cam pins 5 hinder the lens holder 4 from being fitted to the inner periphery of the cam drum 1. Accordingly, it is required that the cam pins 5 be attached from the outer periphery of the cam drum 1 by aligning the rectilinear slots 1a with screw holes for attaching the cam pins 5 after inserting the lens holder 4 into the cam drum 1. For this reason, the work becomes troublesome. At the same time, there arises a possibility wherein declines both in operation of the lens barrel and in optical performance are produced due to a deterioration in attachment of the cam pins 5.